Conditions are favourable for the development of dangerous thunderstorms that may be capable of producing damaging wind gusts.

An approaching cold front is expected to trigger thunderstorms after 2 pm and into the early evening hours. The potential exists for several of these thunderstorms to produce severe weather with winds in excess of 100 km/h being the primary threat.

Very strong wind gusts can damage buildings, down trees and blow large vehicles off the road. Intense lightning is likely with any thunderstorm that develops. Remember, severe thunderstorms can produce tornadoes. Lightning kills and injures Canadians every year. Remember, when thunder roars, go indoors!

Severe thunderstorm watches are issued when atmospheric conditions are favourable for the development of thunderstorms that could produce one or more of the following: large hail, damaging winds, torrential rainfall.

The Office of the Fire Marshal and Emergency Management recommends that you take cover immediately if threatening weather approaches.

Please continue to monitor alerts and forecasts issued by Environment Canada. To report severe weather, send an email to ec.cpio-tempetes-ospc-storms.ec@canada.ca or tweet reports using #ONStorm.

...Lower Great Lakes/Ohio Valley/Mid Mississippi Valley/Central Plains... An upper-level trough will dig quickly southeastward into the Upper Mississippi Valley today. A broad belt of west to west-southwesterly cyclonic flow will be in place ahead of the trough across much of the Great Lakes and Ohio Valley. At the surface, a cold front will advance southeastward today across the central Great Lakes, upper to mid Mississippi Valley and central Plains. A few thunderstorms should be ongoing along the front this morning. Ahead of the front, surface dewpoints are forecast to increase into the mid to upper 60s F by this afternoon. This combined with warming surface temperatures should result in the development of moderate instability. Moderate instability is expected to first develop in the mid Mississippi Valley by late this morning and then spread east-northeastward into the Ohio Valley and southern Great Lakes this afternoon. This will aid convective initiation of surface-based thunderstorms along and just ahead of the front during the 20Z to 22Z timeframe beginning in southern Lower Michigan and far northern Indiana. Thunderstorm coverage should expand quickly west-southwestward along the front during the late afternoon. The development of a linear MCS will be possible by early evening from the Great Lakes west-southwestward into the mid Mississippi Valley.

At mid-levels, a 70 to 80 kt jet max associated with the upper-level trough will translate eastward across the upper Mississippi Valley. This jet max is forecast to increase in strength as it approaches the Slight and Enhanced risk areas. 0-6 km shear is forecast to reach the 40 to 50 kt range along the front as convection organizes late this afternoon. As a result, the combination of instability and deep-layer shear will be favorable for severe thunderstorm development. Although supercells will be possible early in the event, the models suggest that linear development will be favored due to low-level convergence and forced ascent along the front. This will likely make wind damage the greatest severe weather hazard as a line of storms moves southeastward across the region. An enhanced risk for wind damage will be most likely from far eastern Illinois northeastward across north-central Indiana into northwest Ohio, near the southwestern section of a 40 to 50 kt low-level jet. Isolated large hail may also develop with the more discrete rotating storms that develop during the late afternoon, when instability is forecast to be maximized. A marginal threat for hail and strong wind gusts will be possible across southwestern Missouri and southeast Kansas late this afternoon into this early evening.